1. Field of the Invention
This invention relates to a method and device for achieving optical spatial phase modulation. More particularly, it relates to an optical spatial phase modulating device that can be applied to optical correlators, aberration correctors, interferometers and in other such systems.
2. Prior Art Statement
Optical correlators based on the Van der Lugt system are well known. In the van der Lugt system, holographic techniques are used to produce a filter whose phase and amplitude characteristics are matched to the Fourier transform of a reference image. This filter is then used to filter the Fourier transform of a test image, and if the test and reference images contain the same components, then plane waves leave the filter at an angle corresponding to the matching positions of the test and reference components. A further inverse Fourier transform gives an output intensity distribution in which bright spots indicate the positions of matches between objects and reference images.
It has been found recently that if the amplitude information in the filter is discarded and only the phase information is retained, a much sharper correlation may be obtained than is possible with the Van der Lugt filter.
Achieving this requires a filter which modifies only the phase distribution of light passing through it. Furthermore, if this filter were to be made using an optical modulating device which is controlled by a computer, rather than by using a photographic plate or similar recording medium such as in a conventional system, the result would be an extremely flexible and easy-to-use optical processing system.